Telephone system



l. W. GREEN TELEPHONE SYSTEM Filed Dec.

INVENToR J. WGreen/ BY ATTORNEY Aug. 4, 1931.

Patented Aug. 4, 1931 UNITED STATES PATENT OFFICE rRvING W. GREEN, orcRANroRn, JERsEY,AssrGNoR 'ro AMERICAN TELErnoNE AND TELEGRAPH COMPANY,A CORPORATION or NEW YORK TELEPHONE SYSTEM Application led December 21,1928. SerialNo. 327,583.

This invent-ion relates to telephone metering systems, and moreparticularly to means for periodically reversing the direction ofcurrent flow in a telephone circuit to operate Il a meter which recordsthe length of time the telephone is in use. K n

It is an object of this invention to provide a novel, eicient andinexpensive means which is adapted to supply talking., current and 10meter operating current'for such systems and which eliminates thenecessity of using expensive auxiliary apparatus for reversing thedirection of current flow therein to operate the recording device.

The invention comprises, in combination with a telephone meteringsystem, a direct current generator equipped ywith brushes which may be.periodically shifted to reduce thel current produced by the generatorgradk20 ually to Zero and build it up gradually in the oppositedirectiony and a means for periodically shifting said brushes.

The `drawing illustrates diagrammatically a telephone system embodyingthe invention.

i 25 In the drawing, two subscribers stations A and B with subscribersets 1 and 1 are shown With subscribers loops extending to the centraloffice and terminating in the jacks 2 vand 2. As shown, A represents thestation of the 30 calling subscriber and B that of the calledsubscriber. There are located at the stations meters M and M which are'adaptedl to respond to current variations in the subscribers loops. v ys The cord circuit Cy of a central oice is here illustrated as theimpedance coil feed type. Obviously, a cord circuit of the repeatingcoil feed type may be used, if desired. y The cord circuit showncomprises the usual current source 3 grounded at 4, al current supplybridge comprising the impedance coils 5the capacities 6 and 6, the cordconductors 7, 7, 8 and 8 and the supervisory relayk9. Normally, thecurrent supply bridge of the call- .ing subscriber is connected to thesource 3 through the armatures 10 and 10the contacts 11 and 11', and theleads 12 and 12. A switching means 13 is provided to disconnectthecurrent supply bridgeof the calling sub- 50 scriber from the source 3and to connect it to the direct current generator `Gr through thearmatures 10 and 10', the contacts 14 and 14 and the leads 15 and 15.This switching means Which is under the control of relay 9 comprises therelay 16 grounded at 17, the armatures 1() and 10', the conductor 18,the contact 19, the armature 20 and the source 21 grounded at 22.

The direct current generator Gr comprises a magnet v'vith north pole Nand south pole S, the armature 23, the commutator 24 and the brushes25and 26. `The armature 23 is shown as the closed coil ring type andincludes a plurality of coils 27'formin'g a closed circuit With leads 28connecting said coils to Vthe bars of the commutator 24. Other types ofarmatures may be used if desired. Brushes 25 and 26 are positioned so astov be in contact With the opposite sidesof the commutator 24 and arefastened preferably by rocking brush rigging to the collector rings 29andv30,`respectively. The collector ring 30 is supported by the spider31 and the collector ring 29 is, rigidly fastened to the col.- lectorring 30 by the insulated joints 32. Stationary brushes 33and 34 Whichare connected to leads 15 and 15 are positioned so as to be in contactwith collector rings 29 and A36, respectively. The collector rings 29and 30 with the brushes 25 and 26, respectively,are adapted to berotated periodically through a predetermined arc, for example, one-halfrevolution. As shown, the armature rotates in a clockwise direction andthe collector rings and brushes in a counterclockvvise direction. Anarmature of the stationary type With a rotating magnet may be usedWithout departing from the scope of the invention. Any suitable drivingmeans may be used to cause the rotation of the collector rings andbrushes and any suitable means may be provided to regulate the arc andtime of rotation. As diagrammatically shown, the driving means comprisesa continuously revolving motor 35 connected by shaft 36 through afriction clutch 37 to the spider 31 and the regulating means comprises asolenoid 38 which is momentarily energized at predetermined intervals oftime by the clo- 'sure of its circuit which is controlled by the clockmechanism 39. The solenoid has an armature which, in its normalposition, engages one of the stop lugs il which are fastened at oppositepoints on the surface of the collector ring 29. The momentaryenergization of the solenoid 3S attracts its armature. l() and releasesits engagement with the stop lug 41. Immediately thereafter and beforethe collector ring has completed its onehalf revolution, for example,the solenoid is deenergized and its armature is restored t0 its normalposition by means of ribbin spring 42 to engage the other stop lug. Assoon as the stop lug is released from engagement with the armature 40,the collector ring which is under constant tension, due to itsconnection with the continuously revolving motor 35 through the shaft 36and the friction clutch 37, rotates, for example, on-half revolution atsubstantially constant speed until its other stop lug engages thearmature 40. Obviously, the brushes 25 and 26 are rotated at the sametime as the collector rings 9.9 and 30. lt is to be understood that thisinvention is not limited to the particular forms of driving means andregulating means shown, nor to a magnet having only two poles. Acondenser element 49e, preferably of the electrolytic type, is connectedin parallel with the generator circuit through the stationary brushesand e6 to absorb the ripples in the commutator current and to preventany noise that might be caused by generator operation from getting intothe talking circuit.

Although the question of sparking between the brushes and theconnnutator bars is largely a problem of design, several features havebeen embodied in the generator constituting a part of the presentinvention to Aprevent sparking. In ordinary generator, the coils whichare directly under the brushes are momentarily short-circuited. If thebrushes are positioned in the neutral area of the magnetic held-namely,the area in which the coils are not cutting any lines of forcebut aremoving parallel thereto-there is no induced current acting in theshort-circuited coils. At this time, the current in the circuit of theactive coils is flowing through the leads of the short-circuited coils,the `corresponding commutator bars and brushes. Then these commutatorbars pass out from under the brushes, said coils are thrown as perfectlyidle coils into the circuit of the active coils and the current flowingin this circuit will, for an instant, continue to flow through saidleads and said commutator bars and spark across t-he intervening spaceto the brushes. due te the self-induction of said idle coils. On theother hand. if the brushes are placed in a retarded position withrespect to the neutral area of theymagnetic iield and the direction ofrotation, there will be an induced electromotive force acting in theshort-circuited coils, which electromotive force will produce a. largecurrent therein due to the low short-circuit resistance. This currentwill tend to flow in a direction opposite to that of the current in theactive circuit. lhen the commutator bars corresponding to said coilspass out from under the brushes, both the large short-circuited currentand the current of the active circuit will, for an instant, continue toflow from the coinniutator bars to the brushes, due again to theself-induction of the short-circuited coils, and thus cause sparking. Inthe generator disclosed in the drawing, the brushes are placed in anadvanced position with respect to the neutral area of the magnetic fieldand the direction of rotation. Because of this, as the coils pass thebrushes, they, having already passed the neutral area., are beginning toenter the forward magnetic field and to cut the magnetic lines in such away as to tend to set up in them a current in the reversedirection-namely, in the same direction as the current in the circuit ofthe active coils. Hence self-induction will not be present in the coilat this time and no sparking will result. In order to prevent sparkingwhen the brushes are being rotated, carbon brushes having adequatecontact resistance and being large enough to cover at least twocommutator bars are employed. Due to the contact resistance of thecarbon brushes, the resistance of the brushes to the current flowingfrom the commutator bars increases as the areav of contact between thebrushes and the bars decreases. Obviously, this tends to preventsparking. By making each brush large enough to cover several commutatorbars at the same time, part of the current produced by the active coilspasses through the short-circuited coils while it is still under thebrush. Hence, when it passes, out from under the brush, self-induction,as

regards this current, will not be present and there will be no tendencyfor this current to spark across the space between the commutator barand the brush.

As a further safeguard against sparking,

the self-induction of each coil is reduced to a minimum. This isobtained with ay given voltage and current output by employing a maximumnumber of coils, commensurate with practical design, and a correspondingminimum number of turns in each coil. Likewise, the provision ofcomparatively wide pole pieces, as shown, distributes the magnetic fielduniformly over a` large area and avoids concentration at any one point.Other means may be employed to prevent sparking, for example,artificially increasing the resistance of that part of the brush thatlast touches the commutator bars and increasing the resistance of theleads 28.

The operation of the system is as follows: Then the calling subscriberat station A removes his receiver from the hook to initiate a call, theoperator, in response to the signal establishes a connection to thecentral office in the well-known manner. At this time, the current flowsfrom the positive terminal of the source 3 through the lead 12, theContact 11, the armature 10, the upper left impedance coil 5, the cordconductor 7, the jack 2, out over the subscribers loop through the meterand the subscribers set, back through the jack 2, th-e cord conductors8, the lower left impedance coil 5, the armature 10', the contact 11 andlead 12 to the negative terminal of the source 3. After the connectionhas been completed through the cord circuit C to the station B of thecalled subscriber and when the called subscriber removes his receiverfrom the hook, the circuit including the relay 9 will be closed. Theclosure of this circuit and the resulting energization of the relay 9causes the latter to attract its armature 20 which establishes aconnection with the contact 19. The establishment of this connectioncloses the circuit of the relay 16 and causes its energization. Whenenergized,

this relay attracts its armatures 10 and 10 to break their connectionwith the contacts 11 and 11, respectively, and to establish theirconnection with the contacts 14 and 14, respectively. This breaks theconnection of the impedance coils of the supply bridge of the callingsubscriber with the source 3 and connects them to the generator Gthrough the contacts 14 and 14 and the leads 15 and 15. During thisperiod, the generator G is sup-- plying current to the callingsubscribers loop and the source 3 to the called subscribers loop. Atpredetermined intervals of time, for example, every fifteen seconds, theclock mechanism 39 causes the engagement between the armature 40 and thestop lug 41 to be momentarily released and the brushes 25 and 26 arerotated for example, one-half revolution as hitherto described. As theyrotate from their normal position to the midpoints of their arcs ofrotation, the current in the calling subscribers loop is graduallydecreased, due to the bucking of the electromotive force induced in thecoils on the `opposite sides of the armature. At the instant the brushesreach the midpoints of their arcs of rotation, there is no difference inpotential between the brushes and hence the currentin the callingsubscribers loop is zero. When the brushes pass these midpoints, thecurrent is reversed, flowing from the brush 26 through the collectorring 30, the brush 34, the lead 15, the contact 14', the armature 10',the lower left impedance coil 5, the cord conductor 8, the ack 2, outover the subscribers loop, the meter and the subscribers set, backthrough the jack 2, the cord conductor 7, the upper left impedance coil5, the armature 10, the contact 14, the lead 15, the brush 33 and thecollector ring 29 to the brush 25. As the brushes 25 and 26 continue torotate until the one-half revolution, for example, its completed, thereversed current' is gradually` ine creased to its maximum. Thesereversals which occur duringthe conversation at predeterminedintervalsof time take place very rapidly, for example, in .0 1 secondsyand each revolution causes the operationr of the meter located in thecallingsubscribefs loop. The metery located in the called subscribersloop is notl operated due to the fact that the current therein is notreversed.

Although the invention has been described specifically as a currentreversing system, it should be understood that asystem in which thecurrent is variedfroma maximum to zero and back again to a maximum ofthe same polarity is within the scope of this invention.

As shown and described, the generator is connected on one side of thecord circuit only, since, in general, it is desirable to charge the callto the calling subscriberr only. It is obvious, however, that the samemechanism could be applied on the other side of the cord circuit or onboth sides of the cord circuit, if desired, or may be usedin'place ofthesource 3 to supply talking currentr to both subscribers lines. Themechanism shown in the drawing below the dotted lines 43-43 may becommon to all the cords" of a given exchange or to a group of cords or,if desired, may be suppliedv t0 each of the cords separately. Likewise,the connection of the; generator with the cord circuits may be unde` thecontrol of othenmcans than the relay in such a manner that the operationof the meter will begin at any desired time during the connection.

While this inventionA has been illustrated in connection with a typicalcord circuit, using manual operation, it isv apparent that it is equallyapplicable to machine switching apparatus.

What is claimed is: f

` 1. In combination, a; magnet having a plurality of poles, an armatureincluding ka core and a pluralityof coils around saidvcore adapted tohave electromotive force induced thereinby relative rotation betweensaid magnet and said armature, a commutator includ.- ing a pluralityoffbars, saidbars and said coils vbeing electrically connected to oneanother, a pair of collector rings insulated from each other, a pair ofbrushes fastened to said collector rings and adapted to be in electricalcontact with opposite sidesof said commutator, and means forperiodically rotating said collector rings through a predetermined arcto vary the current therethrough. i 4

2, In combination, af magnet having a plurality of poles, an armatureincluding a plurality of coils adapted to have electromotive forceinduced therein by relative rota-r tion between said magnet and saidarmature, the number of said coils having a high ratio to the number ofturns in each coil in the production of a predetermined electromotivete' c.

force therein, a commutator including a plurality of bars electricallyconnected to said coils, a pair of collector rings insulated from eachother, a pair of brushes of high contact resistance fastened to saidcollector rings and positioned so as to be in electrical Contact withopposite sides ci' said commutator along that edge of the magnetic fieldwhich is beyond the neutral area thereof in the direction ot rotation,said brushes being adapted to be simultaneously in contact With aplurality of said commutator bars, a pair of conductors in electricalconnection with said collector rings, and means for periodicallyrotating said brushes through a predetermined are.

3. In a dynamo electric machine, a field magnet, an armature adapted tohave electromotive force induced therein by relative rotation betweensaid magnet and said armature,

a commutator, and a pair of brushes in electrical contact With oppositesides of said commutator and adapted to be rotated periodically througha predetermined arm to vary the current therethrough.

4. In a dynamo electric machine having a iield magnet and an armatureadapted to have electromotive force induced therein by relative rotationbetween said magnet and said armature, a commutator, a pair of brushesin electrical contact with opposite sides of said commutator, a pair ofcollector rings fastened to said brushes, and means Jfor periodicallyrotating said collector rings through a predetermined arm to vary thecurrent therethrough.

5. In a dynamo electric machine having a ield magnet and an armatureadapted to have electromotive torce induced therein by relative rotationbetween said magnet and Said armature, a commutator including aplurality of bars7 a pair of collector rings insulated Jfrom each other,a pair of brushes of high contact resistance fastened to said collectorrings and located so as to be in electrical contact With opposite sidesof said commutator and in an advanced position with respect to theneutral area of the magnetic ield and the direction of rotation, saidbrushes being adapted to be simultaneously in contact with a pluralityof said commutator bars, and means for periodically rotating saidcollector rings through a predetermined arc to vary the currenttherethrough.

In testimony whereof I have signed my name to this specitication this18th day of December7 1928.

IRVING W. GREEN.

